Black hole-neutron star binaries with high spins and large mass asymmetries. II. Properties of dynamical simulations

Black hole (BH)-neutron star (NS) binary mergers are not only strong sources of gravitational waves (GWs), but they are also candidates for joint detections in the GW and electromagnetic (EM) spectra. However, the possible emergence of an EM signal from these binaries relies crucially on the fate of the NS which, in turn, is determined by a complex combination of the equation of state (EOS), the BH spin, and the mass ratio. Depending on these binary parameters, the NS can either undergo a "tidal disruption" or "plunge" directly into the BH without losing its compact structure beforehand. Accurate predictions as to which of these scenarios actually takes place relies on the use of numerical-relativity simulations, which represent essential tools to learn about the properties of the system. In this second paper in a series, we present a systematic exploration of the possible space of binary parameters in terms of the mass ratio and BH spin so as to construct a complete description of the dynamical processes accompanying a BHNS binary merger. This second work relies not only on the initial data of eight nonprecessing spinning binaries presented in the companion paper I, but also on the predictions via quasiequilibrium (QE) sequences on the outcome of the binary. In this way, and for the first time, we are able to relate the predictions of QE analyses with the results of accurate general-relativistic magnetohydrodynamic simulations. In addition to a careful investigation of the evolution of the BH mass and spin as a result of the merger, the total remnant rest-mass of the resulting accretion disk and its properties, and of the corresponding postmerger GW emission, special attention is paid to the conditions that lead to tidal disruption. Leveraging QE calculations, we are able to verify the reliability of stringent predictions about the occurrence or not of a plunge and to measure the "strength" of the tidal disruption when it takes place. Finally, using a novel contraction of the Riemann tensor in a locally orthonormal tetrad and with respect to the one comoving with the fluid introduced in paper I, we are able to point out the onset of the instability to tidal disruption. This new diagnostic can be employed not only to determine the occurrence of the disruption, but also to characterize it in terms of the binary parameters.